Polyamides are well known and have enjoyed tremendous commercial success, particularly in the fiber and bristle industries, as a result of their generally excellent processability and solvent resistance. However, their utility as molding compositions has been hindered as a result of their poor tolerence to moist environments, particularly with respect to their tendency to absorb water, thus gain weight, and to swell or expand.
Polyetherimides, on the other hand, are a more recent class of high performance specialty thermoplastics. Because of their high continuous-use temperatures, inherent flame resistance, low smoke evolution, good electrical properties and generally good physical properties, they are becoming more and more desirable for a wide range of applications requiring such characteristisc, particularly in the high tech electronics industries and in the manufacture of aircraft and the like. However, because of their high temperature characteristics, very high temperatures are needed to process the thermoplastic, e.g. from about 680.degree. to 820.degree. F. Such high temperatures may have a tendency to adversely affect the properties of the polymer. Furthermore, while the polyetherimides have numerous beneficial characterisitics, they are susceptible to premature failure in certain environments.
Recently, Robeson et al (European Patent Appl. 104659) found that by blending polyetherimides with polyamides, one could obtain a composition having improved processability at lower temperatures and better chemical resistance without adversely affecting the excellent mechanical properties of the polyetherimide.
However, the benefits of such blends are not without their detrimental aspects. In particular, while the polyamide brings may benefical characteristics to the blend, it also brings the undesired characteristic of poor tolerence to water, specifically with respect to absorption and expansion. Because of this characteristic, certain applications for the high property profile polyetherimide resins, particularly the high tech electronic applications where part size tolerence is critical, are no longer feasible.
It is therefore an object of the present invention to provide polyetherimide-polyamide compositions having improved tolerence to water or moisture with little, if any, adverse impact on the excellent properties of such blends.